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J^ 8965 



Bureau of Mines Information Circular/1984 




Radiation Hazard Test Facilities 
at the Denver Research Center 



By R. F. Droullard, T. H. Davis, E. E. Smith, 
and R. F. Holub 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8965 



Radiation Hazard Test Facilities 
at the Denver Research Center 



By R. F. Droullard, T. H. Davis, E. E. Smith, 
and R. F. Holub 




UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



Tlia-'iS' 





UNIT OF MEASURE 


ABBREVIATIONS USED IN THIS REPORT 


"C 


degree Celsius 




m 


meter 


cm^ 


cubic centimeter 




mCi 


millicurie 


cm^ /min 


cubic centimeter per 


MeV 


mega electron volt 




minute 




mi 


mile 


ftS/min 


cubic foot per minute 












mln 


minute 


"F 


degree Fahrenheit 




TSQ 


megohm 


gal 


gallon 




mm 


millimeter 


ft 


foot 




ym 


micrometer 


ft3 


square foot 




pCi/L 


picocurie per liter 


hp 


horsepower 




pet 


percent 


h 


hour 




V 


volt 


in Hg 


inch of mercury 




Vac 


volt, alternating current 


km 


kilometer 




in WG 


inch water gage 


L 


liter 




WL 


working level 


L/mln 


liter per minute 










'f]d',2%5 



Library of Congress Cataloging in Publication Data; 



Radiation hazard test facilities at the Denver Research Center. 

(Bureau of Mines information circular ; 8965) 

Bibliography: p. 21-22. 

Supt. of Docs, no.: I 28.27:8965. 

1. Uranium mines and mining— Safety measures. 2. Denver Re- 
search Center (United States. Bureau of Mines). 3. Radon— Measure- 
ment. 4. Nuclear counters— Testing. I. Droullard, R. F. (Robert F.), 
II. Series: Information circular (United States. Bureau of Mines) ; 
8965. 



S^a&SvU't^ 622s [622'. 8] 



83-600315 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Test facilities 2 

Radon test chamber 2 

General description 2 

Chamber 2 

Radon source and control system 4 

Primary air system 5 

Aerosol system 5 

Chamber-Monitoring and data-acquisition system 6 

Measurement and control of radiation 9 

Twilight mine facility 9 

General description 9 

Geology 10 

Surface facilities 12 

Instrument trailer 12 

Mine shop 12 

Mine office 12 

Mine vehicles 14 

Compresser air 14 

Diesel engine 14 

Underground facilities 15 

Ventilation system 15 

Entrance A facilities 15 

Electrical power. 16 

Test sites 17 

Test-site monitoring 17 

Facility utilization 18 

Equipment tests 18 

Training 21 

Conclusions 21 

References 21 

ILLUSTRATIONS 

1 . Radon test chamber 3 

2. Scheme of radon test chamber 3 

3. Chamber access door showing two sampling ports 3 

4. Chamber access door with glove port 3 

5. Front view of radon test chamber showing four sampling ports 4 

6. Radon-sampling port with fittings for tubing 4 

7. Top of radon test chamber showing sampling ports and air pumps 4 

8. Radon flow switching unit 4 

9. Radon flow control system and condensation nuclei air control system 5 

10. Input air filter and humidifier 5 

1 1. Aerosol generating system 6 

12. Continuous working-level detector. 6 

1 3. Continuous radon detector 7 

14. Air flow rate control panels 7 

15. Condensation nuclei monitor and diffusion battery 7 

16. Dosimeter connector rack 8 

17. Switching valves for dosimeter air system 8 



11 



ILLUSTRATIONS— Continued 

Page 

18. Signal-processing Instrumentation 8 

19. Data-acqulsltlon system for radon test chamber 8 

20. Filter being placed Into scintillation counter for alpha-activity 

measurement 9 

21. Location map of Twilight Mine 10 

22. Plan map of Twilight Mine 11 

23. Twilight Mine In 1973 12 

24. Surface facilities located along mine rim road 12 

25. Instrument trailer 13 

26. Interior of Instrument trailer 13 

27. Vehicle entrance to shop building 13 

28. Interior of shop building 13 

29. Interior of mine office building 14 

30. Electric cart 14 

31. One-ton tramming vehicle 14 

32. Small front-end loader. , 14 

33. Bulkhead B 15 

34. Main exhaust fan at Portal B. 15 

35. Small ventilation fan 16 

36. Tag board station 16 

37. Cap -lamp -charging rack 16 

38. Instrumentation room at dosimeter test area 17 

39. Continuous working-level detector at dosimeter test site 18 

40. Continuous working-level detector In exhaust airway 18 

41. Data-acqulsltlon system In Instrument trailer 18 

42. Desk computer system 18 

43. Rapid radon detector undergoing test 19 

44. Passive radon dosimeter undergoing test 19 

45. Alr-cleanlng hard hat undergoing test 19 

46. Alr-cleanlng test site 19 

47. Filter-media test site 20 

48. Cartridge filter tests 20 

49. Prototype air cleaner undergoing tests 20 

50. Demonstration of condensation nuclei counter 21 

51. Trainee using rapid working-level monitor 21 

TABLE 

1. Environmental characteristics of the Twilight Mine 16 



RADIATION HAZARD TEST FACILITIES AT THE DENVER RESEARCH CENTER 

By R. F. Droullard/ T. H, Davis, ^ E, E, Smith, ^ and R, F. Holub'* 



ABSTRACT 

The Bureau of Mines has developed test facilities for use in a re- 
search program that deals with radiation hazards in mining. This report 
describes the radon test chamber located at the Denver Research Center 
and the Twilight experimental mine located near Uravan, CO. 



^Supervisory geophysicist, 
^Engineering technician. 
■^Electronics technician, 
'^Research physicist. 
Denver Research Center, Bureau of Mines, Denver, CO. 



INTRODUCTION 



The Bureau of Mines has been involved 
in studying radiation hazards associated 
with mining for over 20 years. Most of 
the early work was devoted to methods of 
controlling radon and radon daughters in 
underground uranium mine atmospheres with 
particular emphasis on ventilation. In 
the early 1970's, the Bureau expanded its 
research program with a modest increase 
in the number of in-house programs to 
which was added an outside research pro- 
gram conducted by contract. 

The need for a radon test chamber be- 
came evident in the early 1970' s when the 
major in-house research effort was fo- 
cused on instrumentation with emphasis on 
personal dosimeter systems. This work 
requires a carefully controlled environ- 
ment in order to evaluate the accuracy of 
various nuclear radiation detection de- 
vices and methods. 

The first chamber was constructed of 
plywood in the form of a rectangular box 
and it served reasonably well for several 



years. A major problem with the plywood 
box was leakage that permitted room aero- 
sols to enter the chamber. 

A new chamber was designed and con- 
structed starting in the late 1970's, and 
it was placed in operation in early 1980. 
This chamber and its associated compon- 
ents are described in this report. 

The need for an underground uranium 
mine as a test facility for both in-house 
and contractor studies was recognized in 
the late 1960's. The first underground 
facility was developed near Grants, NM, 
in a cooperative effort by industry, the 
State of New Mexico and the Public Health 
Service (6^).^ The Bureau became involved 
with this facility in the early 1970' s 
and used it for a number of contractor 
and in-house studies until 1973 when it 
was decided to develop an underground 
facility where commercial power was 
available. This led to the selection of 
the Twilight Mine that is described in 
this report. 



TEST FACILITIES 



RADON TEST CHAMBER 

General Description 

This facility consists of several com- 
ponents and subsystems listed below and 
described in the report. 

1. Cylindrical chamber. 

2. Radon source and control system. 

3. Primary air system. 

4. Aerosol system. 

5. Chamber-monitoring and data acqui- 
sition system. 

6. Radon-222 and radon daughter mea- 
surement control system. 



Chamber 

Figure 1 shows the front of the cham- 
ber. It has a length of 7 ft, a diameter 
of 5 ft, and a volume of about 137 ft^. 
The walls are made of 0.2-in rolled steel 
with welded seams. The interior and 
exterior surfaces are painted with 
enamel. Figure 2 shows the general 
scheme of the test chamber excluding the 
transducers and data acquisition system. 
Figure 3 shows two sampling ports that 
can be replaced with cover plates. Fig- 
ure 4 shows a second version of the door 
which has a window and a rubber glove 
port. (A viewing window is above the 
port. ) 

-•Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of the report. 



Grab samples for radon-daughter mea- 
surements are usually collected at the 
two stoppered ports shown at the left 
side of figure 5, using a filter holder 
attached to steel tubing. However, in 
special cases, the sampling ports on the 
right-hand side can also be used. Figure 
6 shows a radon sampling port with 



fittings for tubing, located at the left 
end of the chamber. A scintillation cell 
is evacuated with a vacuum pump and then 
switched from the pump to the chamber 
with a three-way valve. An in-line fil- 
ter is used to remove radon daughters 
from the sample. Signals and air lines 
enter and exit the chamber at this site 




Compressed 



FIGURE 1. = Radon test chamber. 



Exhaust 



VI 



2 ngc 

\V2 



KEY 

/ Air pump 

2 Mass flowmeter 

3 Radon test chamber 

4 Mixing chamber 

5 Humidifier 

6 Aerosol generator 

7 Air filter 

8 Chamber radon flowmeter 

9 Radon source control 



Exhaust 



Exhaust 



\ Exh 



'V7 



)V6 



V3 



V4 Si 1/5 



Compressed 
air 



t 



V8 



Room air 

10 Exhaust radon flowmeter 

// Dry radon source 

VI Air control valve 

V2 Chamber exhaust valve 

V3 Chamber input valve 

V4 Bypass valve 

V5 Humidifier valve 

V6 Chamber radon control valve 

V7 Exhaust rodon control valve 

V8 Room air valve 



FIGURE 2. » Scheme of radon test chamber. 




FIGURE 3. - Chamber access door showing two 
sampling ports. 




FIGURE 4o • Chamber accessdoor with glove port. 



on top. Figure 7 shows some of these gas 
ports and several of the air pumps lo- 
cated on top of the chamber. 

As one faces the chamber, air and radon 
gas enter on the right and exit on the 
left through ports located on the central 
axis. The exit port has an 8- by 10-in 
filter to protect the mass flow trans- 
ducers from contamination by the aerosols 
used in the chamber. 

Radon Source and Control System 

Radon-222 is produced from a dry 
radium-226 source with an activity of 
about 2 mCi housed in a lead shield. 
Radon is carried from the source by means 
of compressed air with a regulated flow 



rate of 200 cm^/min. It passes through 
the flow switching unit (fig. 8) and then 
to the chamber or outdoors. An 
electric valve is used to control the 
direction of flow. When radon is desired 
in the chamber, it is switched to the 
radon control panel shown in figure 9 
(upper panel). The pressure gages are 
used to measure volumetric flow rates: 
the one on the right measures the flow 
rate into the chamber, and the one on the 
left measures the flow rate to the out- 
side of the building. This arrangement 
provides control of the amount of radon 
in the chamber atmosphere through adjust- 
ment of metering valves shown on the left 
and right of the panel in figure 9 (fig- 
ure 2, items V6 and V7). Radon levels 
from a few picocuries per liter to 




FIGURE 5. - Front view of radon test chamber 
showing four sampling ports. 



FIGURE 6. - Radon-sampling port with fittings 
for tubing at left end of chamber. 




FIGURE 1 . - iop oi radon test chamber show- 
ing sampling ports and air pumps. 




FIGURE 8. - Radon flow switching unit. 




FIGURE 9. • Radon flow control system (upper 
panel) and condensation nuclei air control system 
(lower panel). 

several thousand picocuries per liter can 
be achieved using this control system and 
by adjusting the flow rate of the primary 
air supply. 

Primary Air System 

The test chamber is operated with a 75- 
L/mln air pump located downstream (fig. 
2) that exhausts to the outside of the 
building. We chose to place the pump in 
the exhaust line rather than in the input 
line primarily to prevent atmospheric 
effects upon the air flow through the 
chamber. The flow rate of this air pump 
is monitored by a mass flow transducer 
(figure 2, item 2) whose signals are con- 
verted to volumetric flow rates. 

Primary air comes from the room either 
by a direct route through valve 8 of fig- 
ure 2 or through a high-efficiency filter 
(figure 2, item 7; figure 10). The input 
resistance of the primary air system is 
low enough to avoid negative pressures in 
the chamber at a flow rate of 75 L/mln. 
If for some reason the chamber air input 
is blocked, a pressure monitor activates 
a safety vacuum valve at -8 in WG, bring- 
ing the chamber back to a zero differ- 
ential pressure. The vacuum valve is 
closed with a manually operated electri- 
cal reset. 




FIGURE 10. - Input air filter and humidifier. 

Aerosol System 

A considerable amount of effort has 
been put into developing an aerosol sys- 
tem that would provide a wide range of 
aerosol concentrations in the chamber 
atmosphere. An aerosol concentration 
range with a minimum of 1,000/cm^ and a 
maximum in excess of 100,000/cm^ is 
desirable for testing the performance of 
instrumentation designed to measure radon 
daughters. In addition, it is necessary 
to maintain a given concentration level 
for extended periods to enable the cham- 
ber atmosphere to reach a steady state. 
The aerosol system shown in figure 11 
meets most of the current requirements in 
this respect. It uses four atomizers, 
described by Leong (_7). Each atomizer 
uses an aerosol source having different 
concentrations of salts. For high aero- 
sol concentrations in the chamber, a 0.1 
pet solution of fluorescein is used, 
lower concentrations use tap water, l-mfj 
resistivity water, and 18-mf2 resistivity 
water. These four solutions provide an 
aerosol concentration range from about 




FIGURE 11. - Aerosol generating system, 

5,000/cm3 to about 200, 000/ cm^. The 
latter two demineralized solutions pro- 
duce aerosols with a mean diameter that 
is smaller than the fluorescein aerosols, 
which have a mean of around 0.07 pm. The 
atomizers are selected by a valve system, 
shown in figure 9 on the lower panel. 

The aerosol generating system is oper- 
ated continuously when the chamber is in 
use. A 1-gal bottle of source fluid 
lasts for several days. It should be 
noted that the atomizers are operated 
with aspiration feed. This method of 
moving the solutions through the atomizer 
is less troublesome than forced-fed sys- 
tems that use air pressure or a high- 
pressure metering pump. 

Chamber-Monitoring and Data- 
Acquisition System 

The radon test chamber is usually oper- 
ated for several days during a test. 
This requires continuous monitoring of 
several parameters related to the chamber 
environment: 

1. Working level. 

2. Radon-222. 



3. Condensation nuclei. 

4. Temperature, 

5. Humidity, 

6. Chamber air flow rate, 

7. Gamma -ray background. 

Working levels are continuously moni- 
tored by a method developed by the Bureau 
0-4^). Figure 12 shows a continuous 
working-level detector inside the cham- 
ber. Two of these detectors are normally 
operated in the chamber during a test. 
Their air flow rate is monitored by a 
mass flow transducer or a volumetric flow 
transducer. In addition, a differential 
flow regulator is used to set the desired 
air flow rate and to hold the flow rate 
constant. 

The radon activity level in the chamber 
is monitored by means of a flow-through 
scintillation cell. Figure 13 shows a 
0.5-L radon detector used to monitor 
radon in the test chamber. Its air sys- 
tem flow rate is controlled by a differ- 
ential flow controller. 




FIGURE 12o =■ Continuous working-level detec- 
tor (upper right). 




FIGURt 13. - Continuous radon detector. 

Air flow rates for the continuous 
working-level detectors and the contin- 
uous radon detectors are visually checked 
by panel-mounted flow meters, shown in 
the panel second from the right in figure 
14. The differential pressure across the 
filters in these monitors is also checked 
with differential pressure gages mounted 
on the panels (fig. 14). 




FIGURE 14. = Air flow rate control panels. 




FIGURE 15. - Condensation nuclei monitor and 
diffusion battery. 

The chamber interior temperature and 
humidity are monitored with a commercial 
system. 



Figure 15 shows the condensation nuclei 
counter used to continuously monitor the 
aerosol concentration in the chamber 
atmosphere. Chamber air is drawn through 
a port in the chamber wall into the 
counter and returned to the chamber 
through another port. The counter is 
also used with the diffusion battery and 
switching valve when aerosol size deter- 
minations are needed. 



The gamma ray background inside of the 
chamber is measured continuously with a 
Geiger-Mueller detector. This background 
information is used to correct the con- 
tinuous working level detectors for their 
response to gamma rays. 

The test chamber contains an air system 
for testing personal dosimeter detectors 



that use filter paper collection of radon 
daughters. Figure 16 shows the 10 con- 
nectors available for attaching a dosim- 
eter to the air system. A 25-L/min 
vacuum pump is connected to a small cham- 
ber, which is coupled individually to the 
connectors in the chamber. The two left- 
hand panels in figure 14, contain the 
flowmeters, differential pressure regu- 
lators, and differential pressure gages 
used in the system. In addition, a set 
of electrically operated valves (fig. 17) 
switches the air system to the dosimeters 
by means of an electrical timer. An 
elapsed timer is used to measure the 
duration of the collection time for the 
dosimeters. This arrangement permits the 
starting of dosimeter tests during the 
period when the chamber is unattended. 



Two muffin-type mixing fans are used in 
the chamber to generate turbulent air 
flows when required. 

Signals from transducers within or ex- 
terior to the test chamber are either in 
analog or digital form. All of the ana- 
log signals are converted to digital with 
commercial analog-to-digital converters 
(fig. 18) which, in turn, are connected 
to scalers. Digital signals are con- 
nected directly to the scalers. 

The data-acquisition system (fig. 19) 
is operated as a parallel system with 
all signals collected over the same 
time period. This method of operation 
is superior to serial data acquisition 
when measurements of random events are 




FIGURE 16. - Dosimeter connector rack. 




FIGURE 17. = Switching valves for dosimeter 
air system. 




FIGURE 18. - Signal-processing instrumentation. 




FIGURE 19. - Data-acquisition system for radon 
test chamber. 



necessary. In application, the system is 
controlled by a recycle timer with a 
selectable delay time. The length of a 
complete sampling cycle is the sum of the 
selected delay time and the length of the 
sample collection period, which is con- 
trolled by a master counter-timer. Data 
output from this system is in the form of 
a printed page and punched tape. A desk 
computer is used to convert the raw data 
from the punched tape to a printout in 
engineering units. 

Measurement and Control of Radiation 

The determination of the activity level 
of radon-222 and radon daughters in the 
test chamber is done by measurement. 
Radon activity levels are measured by 
grab sampling using scintillation cells 
(fig. 6). The efficiency factors of the 
cells are checked by periodic intercal- 
ibration exercises with other laborator- 
ies making radon-222 measurements. 

Radon-daughter measurements for control 
or calibration purposes are made by the 
modified Tsivoglou method (8^). Figure 5 
shows a sampling wand with a filter 
holder being injected into the chamber at 
a sampling port. A sample is collected 
on a membrane filter for 5 min. Total 
volumetric air flow is measured with a 
dry test meter. The differential pres- 
sure across the filter is measured to 
detect a defective filter. 

Radon-daughter activity on the filter 
is measured by placing the collection 
side directly on a zinc sulfide detector 
located within the scintillation counter 
(fig. 20). This figure also shows the 
associated instrumentation located above 
the bench. The counting periods are con- 
trolled by commercial timers programmed 
for the modified Tsivoglou -method timers. 

The alpha detection efficiency for the 
radon daughter detectors is determined 
with Po-214 plated on a stainless steel 
disk which is loaded by electrostatic 
collection of Po-218. The disk activity 
is counted in a gas proportional counter 
of known 2-n efficiency, and in the 
detector being calibrated for a time 




FIGURE 20. - Filter being placed into scintil- 
lation counter for alpha-activity measurement. 

interval sufficient to provide reliable 
data for a regression analysis. 

TWILIGHT MINE FACILITY 

General Description 

The Twilight Mine is operated by the 
Bureau of Mines primarily as a facility 
for studying radiation hazards. It pro- 
vides a testing environment for the 
Bureau's radiation hazards research pro- 
gram that is impractical to duplicate in 
the laboratory or even in most active 
uranium mines. The mine environment is 
controllable without interference to the 
Bureau or to a mining company. In addi- 
tion, the variety and complexity of 
instrumentation needed to effectively 
monitor the mine environment requires a 
permanent installation to avoid unac- 
ceptable amounts of time that would be 
spent on installing and removing equip- 
ment in an active mine. 



10 



The mine is located in the western part 
of Colorado about 10 mi from Uravan, CO, 
and about 83 mi from Grand Junction, CO, 
(fig. 21), The mine site is about 1 mi 
from State Highway 141, and the mine por- 
tals are located in a sandstone rim on 
the western side of a valley formed by 
Mesa Creek. 

Between 1950 and 1971, there was inter- 
mittent production of uranium-vanadium 
ores from the mine. The grade of the ore 
shipped from the property was relatively 
low, and extensive surface drilling 
failed to develop significant ore re- 
serves. In 1973, the Bureau arranged for 
the leasing of the property from Union 
Carbide Corp. , and shortly thereafter, a 
second entry was made to comply with new 
mine safety standards. Figure 22 is a 
plan map of the mine. The original entry 
is at Portal A and the new entry is at 
Portal B. Figure 23 shows the mine at 
the time it was acquired by the Bureau in 
1973. 

Geology 

The Twilight Mine is located in 
the Salt Wash member of the Morrison 
formation (Jurassic), and it is adjacent 
to the Uravan mineral belt, a nar- 
row, crescent-shaped area in south- 
western Colorado. This belt contains 



uranium-vanadium deposits in the Morrison 
formation that have closer spacing, 
larger size and higher grade than in the 
adjoining areas. It is about 50 mi long 
from north to south, and the average 
width is about 5 mi. 

Yellow uranium-vanadium minerals were 
discovered in the Roc Creek locality, 
within a few miles of the Twilight Mine 
in 1881, and the first recorded produc- 
tion came from that area in 1898. The 
ores in the mineral belt were mined until 
1923, principally for radium, with vana- 
dium as a byproduct (from 1936 to 1944 
for vanadium, and from 1948 to the 
present for both uranium and vanadium). 

The Salt Wash member of the Morrison 
formation was formed by streams originat- 
ing on a highland far to the southwest, 
and flowed generally from west to east in 
the Uravan area on a low-gradient allu- 
vial fan or plain of aggradation (_2, 5^). 
Major ore deposits are in thick sand- 
stones laid down in the stream channels 
along the flank of salt anticlines. More 
than 90 pet of the Uravan mineral belt 
ore is mined from the upper rim sandstone 
of the Salt Wash, a composite unit of 
interf ingering sandstone lenses and mud- 
stone seams. The host sandstone is white 
to tan in color, fine-grained, well 
sorted, and contains abundant carbona- 
ceous material, including fossil logs. 




FIGURE 21. - Location map of Twilight Mine. 



Abundance of fossil carbon, which pro- 
vided a reducing environment, and local 
muds tone barriers, which controlled per- 
meability, apparently influenced location 
of ore bodies within the sandstones. The 
remaining mineralized zones in the Twi- 
light Mine seldom exceed 1 ft in thick- 
ness, but there are indications that ore 
rolls, with thickness in excess of 3 ft, 
have been extracted in a few portions of 
the mine workings. 

The ore minerals in this mine are 
of the secondary type and include 
tyuyamunite and corvusite. Small amounts 
of copper minerals are associated with 
the uranyl vanadate suite. 



11 



LEGEND 

IRI Power center 

IR2 Cort-chorging system 

ILI Protective-clothing orea 

1L2 Storooe oreo 

IL3 Tractor-charging center 



Test site 

IR3 

IR5 

IR5-I 

IR5-2 

IR6 

IR7 

IRS 

IL4 

IL5 

IL6 

IL6-I 

IL6-2 

IL7 

IL8 

IL9 

ILIO 



2RI 

2R2 

2R3^ 

2R4 

2R5 

2R6 



3RI 

3R2 

3R3 

3R4 

3LI 

3L2 

3L2-1 

3L2-2 

3L2-3 

3L2-4 

3L3 

3L4 

3L5 

3L6 

3L6-i 

3L5-2 

3L6-3 

3L6-4 

3L6-5 

3L6-6 

3L7 



Width, 
ft 

10 

10 
10 
8 
10 
10 
15 
20 

10 
20 
30 
30 

15 
10 



15 
10 
10 
10 
10 
10 



10 
10 
10 
20 
10 

10 
10 
10 
10 



20 
20 
10 
10 
10 
10 
20 



Length, 
ft 
25 

25 
30 
40 
25 
55 
50 
50 

20 
20 
65 
25 



35 
7 
25 
27 
35 
55 



15 
5 
5 

15 
5 

5 
30 
15 

5 
35 
115 
20 



10 
35 
30 
30 
10 
20 



3L6-5 




>/\Air compressor 
Portal B 



I Portal A 

I I Shop 
Instrument trailer 



FIGURE 22. - Plan map of Twilight Mine. 



Eight ore samples from the Twilight 
Mine were measured to determine their 
radon emanation coefficient (1). The 
results range from 13 to 32 pet and are 
typical of other ores from the Uravan 
Mineral Belt, which have a mean emanation 
coefficient of 19.5 pet. 



The sandstone is highly fractured with 
a major fracture pattern that trends 
northwest-southeast. These fractures 
have a significant effect on the radon 
levels in the mine. Declining barometric 
pressures tend to pump radon from frac- 
tures, which serve as reservoirs for the 
gas. 



12 




FIGURE 23. . Twilight Mine in 1973. 

Surface Facilities 

Major surface facilities installed by 
the Bureau include an instrument trailer, 
an office building, and a shop for main- 
tenance, all of which are located at Por- 
tal A. An air coinpressor and a diesel 
engine are located at Portal B, Figure 
24 shows most of the surface facilities 
that are located along a rim road. 

Instrument Trailer 

The instrument trailer is an 8-ft by 
40-ft van (fig. 25) that was modified 
into a mobile laboratory. It contains a 
central air conditioner and heating sys- 
tems operating on propane gas. Labora- 
tory furniture includes, work benches, 
cabinets, drawers, and a hood that draws 
its air supply from outside of the 
trailer. Figure 26 shows an interior 
view of the trailer. 

The trailer serves as a data acquisi- 
tion and processing center for the mine 




FIGURE 24. - Surface facilities located along 
mine rim road. 

and one of several storage areas for 
project supplies. 

Mine Shop 

Figure 27 shows an exterior view of the 
mine shop building. This metal building 
has about 320 ft^ of floor area and 
serves as a maintenance and storage 
facility. It has a forced-air heating 
system and a variety of shop equipment 
including an air compressor, gas and 
electric welders, and several types of 
power tools. Figure 28 is an interior 
view of the shop. 

Mine Office 

The plan map (fig. 22) shows the lo- 
cation of the mine office building, a 
14- by 20-ft structure that serves as 
an office and a project work site. 
Figure 29 is an interior view of this 
facility. 



13 





FIGURE 25. - Instrument trailer. 



FIGURE 26. - Interior of instrument trailer. 





FIGURE 27. - Vehicle entrance to shopbuilding. FIGURE 28. - Interior of shop building, 



14 





FIGURE 29. - Interior of mine office building. 



FIGURE 30. - Electric cart. 





FIGURE 31. - One-ton tramming vehicle. 

Mine Vehicles 

Several types of vehicles are in use at 
the mine: A crawler tractor with a load- 
ing bucket, two electric carts (fig. 30), 
a 1-ton rock-tramming unit (fig. 31), and 
a small front end loader (fig. 32). 

Compressed Air 

A 300-ft2/min air compressor is located 
in a metal building near Portal B, 
The compressor is driven by an electic 
motor and the main compressed air line 
runs from the compressor through B 




FIGURE 32. - Small front-end loader. 

haulageway to a point near test site 1R5 
(fig. 25). 

Diesel Engine 

A diesel engine located near the build- 
ing that houses the air compressor is 
used to generate diesel smoke. The ex- 
haust from this unit is carried by pipes 
to the vicinity of bulkhead B (fig. 33) 
for injection into the mine atmosphere. 



15 





FIGURE 33. - Bulkhead B. 



FIGURE 34. - Main exhaust fan at Portal B. 



Underground Facilities 

Ventilation System 

The primary ventilation system for the 
mine is located at Portal B. Two 20-hp 
vane-axial fans are installed back- 
to-back. The innermost fan (fig. 34) is 
the exhaust fan, which is operated most 
of the time. Occasionally, the ventila- 
tion is reversed for special tests and 
the outermost fan is operated. These 
fans are equipped with an automatic re- 
start system. In the event of a power 
failure, the operating fan will restart 
as soon as all three phases of power are 
available. 



Smaller fans are used at various sites 
to control radon-daughter levels. Figure 
35 shows a 1/2-hp fan installed near test 
site 1R7. Air from this fan is directed 
to the instrument room located at test 
site 1L8. A similar fan provides venti- 
lation air for the instrument room lo- 
cated at test site 1L7. This fan draws 
air from the surface through a borehole 
that has been cased. 

Not all areas of the mine are venti- 
lated; unventilated areas are marked with 
warning signs. 

Table 1 lists the environmental charac- 
teristics of the mine atmosphere. 



A secondary ventilation fan is located 
at bulkhead B, this is a two-stage vane 
axial fan with two 7-1/2-hp motors. One 
or both motors can be used to provide 
various air flows through the mine work- 
ings that begin at test site 1L9 and 
return to test site 3R1. 



Entrance A Facilities 

A tag board (fig. 36) is located at 
mine site IRl . Everyone entering the 
mine is required to tag-in at this point. 
Visitors without personal tags use num- 
bered tags available at this site. Hard 



16 



TABLE 1. - Environmental characteristics of the Twilight Mine 

Underground temperature ...."F.. 52-65 

Underground relative humidity.... pet.. 25-95 

Radon-222 levels .pCi/L.. to 80,000 

Radon-daughter activity^ WL.. to 800 

Condensation nuclei per cubic centimeter ~200 to 10^ 

Average ventilation air volume ft^/min.. 13,000 

Volume of mine opening ft 3.. ~300,000 

Host rock effective permeability darcys.. 1 x 10** 

Absolute barometric pressure in Hg.. 24.6 to 25.6 

Altitude of portal A.... ft.. 5,000 

^ 1 WL is any combination of radon daughters per liter of air 
which, in decaying completely through polonium-214, will result 
in the emission of 1.3 x 10^ MeV of alpha energy. 

hats, cap-lamp belts, self -rescuers, used only occasionally to supplement the 
safety glasses, and respiratory masks are regular mine lighting system, 
also available here for visitors. The 

cap-lamp -re charging rack (fig. 37) is A major first aid station located at 
located at site IRl. These lamps are the entrance to mine (site 1L2) also 

serves as a storeroom for mine supplies. 

A 1,000-gal water storage tank and 

^^^^^^"''^^^^" electric pressure pump are located at 

mine site 2R1. The water is supplied 
to the surface facilities during the 
months when the low temperature remains 
above freezing. Water for this tank is 
purchased from a local water service 
frf^^^^^^^ that hauls it from Nucla, CO, 30 miles 
away. 

Electrical Power 

One of the primary reasons for select- 
ing the Twilight Mine was the availabil- 
ity of commercial electrical power. When 





FIGURE 36, = Tag board statiotio 



FIGURE 37. = Cap=lamp=charging racko 



17 



the mine was leased, the existing power 
line was extended to a point above en- 
trance A. Three-phase, 440-Vac service 
was brought into the mine at this en- 
trance, and the main disconnect switch 
was established at the IRl mine site. 
From this point, the 460-Vac line is con- 
verted to 230-Vac and 115-Vac service, as 
required at various sites in the mine and 
at the surface. 

Electric power interruptions are not 
uncommon at the mine. Usually they are 
momentary, but of sufficient duration to 
require automatic starting of data- 
acquisition systems and, the mine venti- 
lation fans. 

Test Sites 

Three major test sites in the mine are 
monitored for various physical parameters 



on a continuous basis. These sites, 
shown in figure 25, are called dosimeter 
test area, air-cleaning test area, and B 
haulage test area. Two of the test 
sites, dosimeter and air cleaning, have 
instrumentation rooms that are heated 
during the colder months of the year. 
Figure 38 shows some of the instruments 
for measuring radon daughters by grab 
sampling in the room at the dosimeter 
test area. 

Bulkhead A is located at the en- 
trance to the dosimeter test area. 
Bulkheads A and B are used to con- 
trol air flow for a variety of tests 
that include dosimeter performance, air- 
cleaning-filter efficiencies, and the 
effects of over-pressure on radon 
levels. 

Test-Site Monitoring 




FIGURE 38. " Instrumentation room at dosim- 
eter test area. 



Radon and working levels are measured 
continuously at the three test sites. 
Figures 39 and 40 show two examples of 
Bureau-developed continuous working-level 
detectors. In addition, two of the sites 
(3R1, 1L8) are measured for relative 
humidity and temperature. The venti- 
lation air velocity is continuously 
measured at the B haulage test site 
ILIO. 

Signals from the underground instru- 
ments are brought to the instrument 
trailer at the surface by coaxial cables. 
Figure 41 shows the primary data- 
acquisition system for the Twilight Mine. 
The raw data is converted to engineering 
units by a small desk computer (fig. 42). 
Unless a specific study is being con- 
ducted, the data system takes 40-inin sam- 
ples of each parameter being monitored 12 
times in 24 hr. The raw data is pro- 
cessed once a week at the Denver Research 
Center. 



18 





FIGURE 39. - Continuous working-level de- 
tector at dosimeter test site. 



FIGURE 40. - Continuous working-level de- 
tector in exhaust airway. 





FIGURE 41. - Data-^acquisition system in in= 
strument trailer. 



FIGURE 42. - Desk computer system. 

Facility Utilization 

Equipment Tests 

The Twilight Mine serves primarily as a 
facility for testing the performance of 
radiation-exposure-measuring instruments 
and the evaluation of control technol- 
ogies for airborne radiation in a typical 
mine envioronment. 



19 



Instrumentation for measuring radon and 
radon daughters has been frequently 
tested in the mine to determine accuracy 
and reliability. Figure 43 shows a rapid 
radon monitor undergoing tests for per- 
formance after receiving it from a con- 
tractor. Figure 44 shows several commer- 
cial radon dosimeters (lower right, below 
suspended filter holder) being monitored 
by a continuous radon detector at test 
site ILIO. Figure 45 shows a hard hat 
with a face shield undergoing tests for 



effectiveness in removing radon daughters 
from the wearer's breathing zone. The 
hard hat contains an air system with a 
filter for removal of dust and airborne 
radioactivity. A continuous working- 
level monitor in the mouth region of the 
simulated head measures the radon- 
daughter activity. 

Studies of radiation hazard control in 
the facility have included overpressure 
using the portion of the mine north of 





FIGURE 43. - Rapidradondetector undergoing test. 



FIGURE 44. - Passive radon dosimeter under- 
going test (lower right). 










i' 1 


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^'■' '^^^^^^^^S^^K wmf^-- 



FIGURE 45. - Air-cleaning hard hat undergoing 
test. 



FIGURE 46. - Air-cleaning test site. 



20 





FIGURE 47. - Filter=media test site. 



FIGURE 48. = Cartridge filter tests. 




FIGURE 49. = Prototype air cleaner undergoing 
tests. 



bulkheads A and B; wall sealants at test 
sites 1R5, 1R6, and 1R7 bulkheads to seal 
old workings at 1R5, 1R6, and 1R7 ; and 
air cleaning at test site 1L8. 

Figures 46-48 show an air-cleaning sys- 
tem installed to evaluate filter media 
for effectiveness in removing airborne 
radioactivity and life expectancy under 
typical mine conditions. Figure 49 shows 
a prototype air cleaner developed under 
contract undergoing performance evalua- 
tion tests at the air-cleaning site in 
the mine. High levels of dust, diesel 
smoke, and airborne radioactivity are 
generated in the portion of the mine 
north of bulkheads A and B. Air contain- 
ing these materials is ducted to the air- 
cleaning systems under test. 



21 




FIGURE 50. • Demonstration of condensation 
nuclei counter. 

Training 

Training sessions related to the mea- 
surement and control of radiation hazards 
in mining are conducted several times a 
year in this facility. Personnel receiv- 
ing the training represent industry, and 




FIGURE 51. • Trainee using rapid working-level 
monitor. 

both State and Federal Governments. The 
training is conducted jointly by the Mine 
Safety and Health Administration (U.S. 
Department of Labor) and the Bureau of 
Mines. Figure 50 shows a demonstration 
of a condensation nuclei counter, and 
figure 51 shows a trainee using a rapid 
working-level monitor. These training 
sessions provide hands-on experience for 
the participants in the use of several 
types of instruments. 



CONCLUSIONS 



The test facilities described in this 
report are considered essential to the 
Bureau's radiation hazards research pro- 
gram. The radon test chamber provided 
the controlled environment needed for 
instrumentation and methods evaluation. 



The Twilight Mine provided a typical 
uranium mine environment for evaluating 
methods of radon-radon daughter control. 
Both of the facilities serve as training 
centers for government and industry 
personnel. 



REFERENCES 



1. Austin, S, R. , and R. F, Droullard. 
Radon Emanation From Domestic Uranium 
Ores by Modification of the Closed-Can 
Gamma-Only Assay Method. BuMines RI 
8264, 1978, 74 pp. 

2, Craig, L. C, C. N. Holmes, and 
R. A. Cadigan. Stratigraphy of the Mor- 
rison and Related Formations, Colorado 
Plateau Region. U.S. Geol. Surv. Bull. 
1009E, 1955, pp. 125-168. 



3. Droullard, R. F., and R. F. Holub. 
Continuous Working Level Measurements 
Using Alpha or Beta Detectors. BuMines 
RI 8237, 1977, 14 pp. 

4. Droullard, R. F., and R. F. Holub 
(assigned to U.S. Dep. Interior). Meth- 
od of Continuously Determining Radia- 
tion Working Level Exposure. U.S. Pat. 
4,185,199, Jan. 22, 1980. 



22 



5. Fischer, R. P., and L. S. Hilpert. 
Geology of the Uravan Mineral Belt. U.S. 
Geol. Surv. Bull. 988-A, 1952, 13 pp. 

6. Kaufman, E, L,, and R. E. Din- 
widdle. Project Dakota — A Uranium Mine 
Atmosphere Research Laboratory. NM 
Health and Social Services Dep., 1969, 
21 pp. 



7. Leong, K. H, , H. C. Wang, S, J. 
Stukel, and P. K. Hopke. An Improved 
Constant Output Atomizer. AIHA J. , v. 43, 
No. 2, Feb. 1982, pp. 135-136. 

8. Thomas, J. W. Measurement of Radon 
Daughters in Air. Health Phys., v. 23, 
1972, pp. 783-789. 



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